Ascension Island HDAS
HDAS Horizontal Directional Drilled Export Cable Shore Landing, Ascension Island
The Hydroacoustic Data Acquisition System (HDAS) is the marine element of the worldwide system for monitoring for clandestine nuclear tests for the Comprehensive Test Ban Treaty Organization (CTBTO). SST was contracted by NFESC to support the installation of systems at Wake Island in the Pacific Ocean and at Ascension Island in the Atlantic Ocean. Both sites are very remote and presented challenging logistics requirements. SST’s role included design of the shore landings, marine engineering and bathymetric survey, both in near-shore shallow water as well as in full ocean depth, and installation of the HDD shore ends.
SST’s responsibilities included preparation of a Desktop Study, recommendation for the shore landing site, planning and management of the shore end and deepwater surveys, and selection of cable routes. Three subsurface conduits were installed at Southwest Bay, Ascension Island, to protect three HDAS cables coming ashore. This system by-passes the sea-shore interface and high energy surf zone, which poses the greatest hazard to the survivability of cables at the shore landing.
Three Directionally Drilled Boreholes, 470, 570, and 820 feet in length, exiting the seafloor at water depths of 35 feet or greater, bring the system cables ashore protected from the nearshore environment.